Voltage stabilizing device for electric drill motor

ABSTRACT

A voltage stabilizing device for an electric drill motor used in a well comprises a voltage control unit provided in the motor connected between a power supply source and current leads of the motor; a voltage transducer in the motor incorporating at least two current transformers having primary winding separately connected to two different ones of the current leads; a voltage transformer connected to the two different ones of the current leads, a plurality of resistors, the current transformers having secondary winding shunted by the resistors having resistances proportional to the total resistance to the corresponding current lead and being connected in series to each other, and to the secondary windings of the voltage transformer, the output of the transducer being essentially a geometrical sum of the voltage transformer, the output of the transducer being essentially a geometrical sum of the voltage of the current leads and the voltage drop across the current lead and being proportional to the motor voltage; a comparison unit adapted to compare a reference voltage proportional to the voltage to be stabilized with the outer voltage of the transducer, the output of the comparison unit being connected to the voltage control unit for controlling the operation of that unit.

United States Patent 72] Inventors Izrail Mordukhovich Pesis ulitsaMetallistov, 10, kv. 12; David Leonidovich Shvarts, ulitsa Olminskogo,10, kv. 2, both of Kharkov, U.S.S.R. [21] Appl. No. 833,967 [22] FiledJune 17, 1969 [45] Patented Oct. 19, 1971 [32] Priority July 19, 1971[33] U.S.S.R. [31] 1254002 [54] VOLTAGE STABILIZING DEVICE FOR ELECTRICDRILL MOTOR 4 Claims, 2 Drawing Figs.

[52] US. Cl 318/344, 318/348, 323/20 [51] lnt.Cl 1102p 5/18 [50] Fieldof Search 318/342, 344, 347, 348; 322/25; 321/18, 24, 25; 323/7, 9, 79,80, 20

[ 56] References Cited UNITED STATES PATENTS 2,981,882 4/1961 Rosenblatt322/25 X 3,077,556 2/1963 Graf 318/347X Primary Examiner-Cris L. RaderAssistant Examiner-H. Huberfeld Attorney-Waters, Roditi, Schwartz &Nissen ABSTRACT: A voltage stabilizing device for an electric drillmotor used in a well comprises a voltage control unit provided in themotor connected between a power supply source and current leads of themotor; a voltage transducer in the motor incorporating at least twocurrent transformers having primary winding separately connected to twodifferent ones of the current leads; a voltage transformer connected tothe two different ones of the current leads, a plurality of resistors,the current transformers having secondary winding shunted by theresistors having resistances proportional to the total resistance to thecorresponding current lead and being connected in series to each other,and to the secondary windings of the voltage transformer, the output ofthe transducer being essentially a geometrical sum of the voltagetransformer, the output of the transducer being essentially ageometrical sum of the voltage of the current leads and the voltage dropacross the current lead and being proportional to the motor voltage; acomparison unit adapted to compare a reference voltage proportional tothe voltage to be stabilized with the outer voltage of the transducer,the output of the comparison unit being connected to the voltage controlunit for controlling the operation ofthat unit.

20 24 25 21 "4 Term PATENTEUUBT 19 IHYI FIGZI VOLTAGE STAIILIZING DEVICEFOR ELECTRIC DRILL MOTOR The present invention relates to voltagestabilizing devices for an electric drill motor operating in a well at aconsiderable distance from the power supply source.

Known in the art is that due to a variable load on the electric drillmotor the voltage across the terminal thereof varies continuously. Topreclude frequent stoppings of the motor with the decrease of thevoltage across its terminals it is necessary to diminish the load on theelectric drill involved which in turn results in decreased efficiency ofdrilling.

To diminish the effect of voltage variations use is made of a voltagestabilizing device provided across the terminal of the electric drillmotor in question. Such a device incorporates a voltage control unitbased upon saturation chokes which is provided beyond the well and isconnected to the wires of the current leads between the power supply andthe electric drill motor involved. The operation of the above-mentionedvoltage control unit is controlled by a feedback system which features acurrent and voltage transducers within the wires of the current leadsand a comparison unit adapted to compare a reference signalcorresponding to the voltage to be stabilized and the output voltage ofthe transducer. The transducer is based on two current transformersinterconnected to one of the wires of the current leads, and a voltagetransformer connected to two wires of the current leads.

The output signals from each transformer are converted into DC signalswhich are algebraically summed and compared with the reference signal inthe comparison unit adapted to control the voltage regulation unit.

The voltage drop across the chokes varies depending upon the outputsignal from the comparison unit and thus the voltage across the motorterminals is controlled.

Since in the process of operation of the electric drill there alwaysexists a phase difference between the current and voltage that variesdepending upon load involved, the output signal from the comparison unitobtained as a result of comparing the algebraic sum of the transformeroutput signals and the reference signal, does not correspond to the truevoltage variation across the motor terminals. Due to the abovesaid theaforementioned device fails to provide the desired accuracy of voltagestabilization.

The accuracy of voltage stabilization may be improved due to theintroduction of a special nonlinear element which would be capable oftaking the account of the phase difference between the current andvoltage involved.

However implementation of such element is complicated and besides, itsutilization complicates the design of the entire stabilizing device andprovides great difliculties in service when motors with differentperfonnance are involved.

it is the main object of the present invention to improve the accuracyof the operation of the voltage stabilizing device acrossth'e terminalsof the electric drill motor, that can be employed in the operation ofvarious electric motors irrespective of their performances.

This and other objects of the invention are accomplished by the factthat in the device for voltage stabilization across the terminals of theelectric drill motor, comprising a voltage control unit connected to thewires of the current leads between the power supply source and the motorand controlled by the feedback system whose output is essentially acomparison unit adapted to compare the reference voltage proportional tothe voltage to be stabilized, and the output voltage from the stabilizevoltage transducer featuring at least two current transformers and avoltage transformer, according to the invention, the primary windings ofthe current transformer are connected to two difierent wires of thecurrent leads that likewise connect the primary windings of the voltagetransformer while connected to the comparison unit are both thesecondary windings of the voltage transformer and the secondary windingsof the current transformers connected in series to said secondarywindings of the voltage transformer and shunted by the resistors whoseresistances are proportional to the total resistance of the wires of thecurrent leads. It is reasonable that the proportionality factor beselected equal to the product of the transformation ratios of thecurrent and voltage transformers.

The advantage of the contemplated device lies in the fact that thetransducer thereof based on resistors adapted to shunt the secondarywindings of the current transformers provides voltages which practicallycoincide with the phase of voltage drops across the wires of the currentleads. Taking into account that the voltage transformer featurespractically inconsiderable phase error and series connection of thesecondary windings of the voltage and current transformers shunted bythe resistors provides the obtaining of a geometrical sum of voltages,the voltage at the output of the feedback transducer is exactlyproportional to that across the motor terminals. This fact provides highaccuracy of voltage stabilization. The invention will be describedhereinbelow by way of illustration of an exemplary embodiment thereofwith due reference to the accompanying drawings wherein:

FIG. 1 represents an elementary diagram of the voltage stabilizingdevice, according to the invention, and

FIG. 2 represents a voltage vector diagram explaining operation of thevoltage transducer at the electric drill terminals.

A sinkable electric motor 1 (FIG. I) of the electric drill (not shown inthe drawing) by wires 2, 3 and 4 of the current leads is connected tothe power supply source through a voltage control unit 5. The voltagecontrol unit 5 includes power chokes 6 with diodes 7 exhibiting aninherent positive feed back. The above-mentioned chokes are adapted tocompensate for a voltage variation in the electric motor 1 in theprocess of its operation within the well that may occur both due tocurrent or voltage variation of the power supply source and due to thechange of the load on the electric motor I. The control of the operationof the unit 5 is effected by the feedback system incorporating a voltagetransducer 8 provided in the electric motor 1 and a comparison unit 9adapted to com pare the reference voltage proportional to the presetvoltage of the electric motor, with the output voltage of the transducer8 which is proportional to the true voltage across the terminals of theelectric motor 1. The unit 9 includes semiconductor components andserves in addition as an amplifier.

The transducer 8 comprises two current transformers I0 and 11 and avoltage transformer 12. A primary winding 13 of the transformer 10 isconnected to the wire 4, whereas the primary winding 14 of thetransformer 11 is connected to the wire 3. The primary winding 15 of thevoltage transformer 12 is connected to the wires 3 and 4. The secondarywindings l6, l7 and 18 of the above-mentioned transformers with dueaccount of the polarity are interconnected in series. In this case thesecondary windings l6 and 17 of the current transfonners are shunted byresistors 19 and 20.

The value of the resistance of the resistors 19 and 20 are selecteddepending upon the total resistance of the corresponding wire of thecurrent leads so as to provide a voltage at the transducer output whichis proportional and coinciding with respect to phase to the voltageavailable across the terminal of the electric drill in question.

The voltage U across the resistor 19 is calculated from the followingfonnulas below:

R131. where i is the current flowing through the resistor 19 featuringthe resistance R,,; i is the current flowing through the wire 4, and Kis the transfonnation ratio of the current transformer 10.

The voltage U at the secondary winding 18 of the transformer 12 iscalculated from the following formulas below:

where U is the voltage across the wires 3 and 4 of the current leads,and

K is the transformation ratio of the transformer 12. To provide thehereinabove stated conditions which ensure geometrical summing up of thevoltages across the wires of the current leads and the voltage dropacross said wires, it is required that where U, is the voltage dropacross the wire 4, and Z is the total resistance of the wire 4.Comparing the (l) and (3) we obtain The value of the resistance R iscalculated analogously where K is the transformation ratio of thecurrent transformer 11. Thus, the resistance of the shunting resistorsis approximately equal to the product of the total resistance of thecorresponding wire of the currents leads on the transformation ratiosbetween the corresponding current and voltage transformers.

Since the device in contemplation may be utilized in operation with theemployment of various current leads, featuring naturally difi'erenttotal resistances the resistors 19 and 20 are variable.

The electric circuit formed by the series-connected secondary windingsof the transformers, is connected to the rectifying bridge 21incorporating two capacitors 22 and 23, and a choke 24. The output ofthe rectifying bridge 21 through the resistor 25 is connected to thecomparison unit 9 which includes a semiconductor transistor 26, thepositive pole of the bridge being connected to the base, whereas thenegative pole is connected to the emitter.

The power supply source of the reference voltage proportional to thepreset voltage to be stabilized in the electric motor 1, is connected tothe comparison unit 9 through the adjustably potentiometer 27 and theresistor 28. In this case the positive pole of the reference voltagesupply source is connected to the emitter and the negative pole isconnected to the base of the transistor 26.

The switching polarity of the rectifying bridge and the referencevoltage supply source may be reversed but in any case the emitter andthe base should be connected to the poles of the bridge and thereference voltage supply source, featuring unlike polarity.

The output of the comparison unit 9 is connected to the control windings29 through the resistors 30 of the power chokes 6.

Let us consider operation of the contemplated device.

Let us suppose that the voltage U across the terminals of the electricmotor 1 of the electric drill is equal to the voltage to be stabilized.This voltage is in fact a geometrical sum of the voltages across thewires 3 and 4 nearby the output of the unit and phase voltage drops U,and U across the wires 3 and 4. As referred to FIG. 2 corresponded tosaid voltages are the vectors U,, U, U, and U Within the transducer 8across the resistors 19 and whose values are selected according to theabove-mentioned formulas there produced the voltages proportional to thephase voltage drops U, and U across the wires of the current leads, thevoltage across the resistor 19 coincides in phase with the voltage Uwhile the voltage across the resistor 20 is in antiphase with thevoltage U: (without taking account of the current transformer errors).The voltage U available at the output of the transformer 12 isproportional and coincides in phase (without taking account of thetransformer error) with the voltage across the wires 3 and 4. Thevoltage U available at the input of the rectifying bridge 21 isessentially a geometrical sum of the voltages U U and U As referred toFIG. 2 corresponded to said voltages are the vectors U 20 U18 and 2i- Itfollows that the vectors U and U U, and U U;, and U are pairwisecolinear and their scalar values are proportional and, consequently, thevectors U and U are likewise colinear and their scaler values areproportional. Consequently, the voltage at the input of the rectifyingbridge 21 is proportional to the voltage across the terminals of theelectric motor 1 of the electric drill involved. Corresponded to saidvoltage is a certain voltage U When the electric drill operates, thevoltage variation across the terminals of its electric motor may be dueto two reasons which are involved both or occur separately: due tovariation of the load on the electric motor 1 and due to voltagevariation of the power supply source. Corresponded to said variationsare voltage variations U U and U;, and proportional variations of thevoltages U U and U Since it has been already shown that the vectors Uand U are colinear and their scalar values are proportional, we mayprove that with variations of the aforementioned voltages the voltage atthe input of the rectifying bridge 21 will vary similar to the voltagevariation across the terminals of the electric drill motor.

The voltage U from the output of the rectifying bridge 21 is suppliedthrough the resistor 25 to the input of the comparison unit 9, which issimultaneously supplied through the resistor 28 with the referencevoltage U which is proportional to the voltage U, under stabilization.Depending upon the difference between the voltages U and U thecomparison unit 9 produces a signal according to which the currentflowing through the control windings 29 varies with the resultantvoltage drop across the power chokes 6.

According to the variation of the voltage drop across the chokes 6 thevalues of the voltages U U and U, U U and U and consequently, thevoltages U,and U,,across the terminals of the motor and across therectifier, will start to vary, too; when the voltage becomes equal tothe reference voltage U the comparison unit 9 will not produce thesignal to vary the current through the chokes 29 which means that thevoltage U across the motor terminals has reached the preset valuesubject for stabilization.

The employment of the herein-disclosed invention provides thepossibility to substantially increase the accuracy of voltagestabilization and simplify the design of the entire device.

What is claimed is:

l. A voltage stabilizing device for an electric drill motor in operationin a well, supplied by a power supply source and having three currentleads comprising: a voltage control unit provided in said motorconnected between the power supply source and the current leads of saidmotor; a voltage transducer in said motor, incorporating at least twocurrent transformers having primary windings separately connected to twodifierent ones of the current leads; a voltage transformer connected tosaid two different ones of said current leads, a plurality of resistors,said current transformers having secondary windings shunted by saidresistors having resistances proportional to the total resistance of thecorresponding current lead and being connected in series to each otherand to the secondary windings of the voltage transformer, the output ofthe transducer being essentially a geometrical sum of the voltagesacross the current leads and the voltage drop across said current leadsbeing proportional to the motor voltage; a comparison unit adapted tocompare a reference voltage proportional to the voltage to be stabilizedwith the output voltage of said transducer, the output of saidcomparison unit being connected to the voltage control unit forcontrolling the operation of said control unit.

2. A device as claimed in Claim 3, wherein the resistance of each of theshunting resistors is where,

Z is the total resistance of the wire to which the resistor isconnected,

K, stands for the transformation ratio of the current transformer, and

3. A device as claimed in claim 1, wherein said resistors are variable.

4. A device as claimed in claim 1, including a full wave rectifierconnected across the output of said transducer. 21

filter unit.

coupled between said transducer and said comparison

1. A voltage stabilizing device for an electric drill motor in operationin a well, supplied by a power supply source and having three currentleads comprising: a voltage control unit provided in said motorconnected between the power supply source and the current leads of saidmotor; a voltage transducer in said motor, incorporating at least twocurrent transformers having primary windings separately connected to twodifferent ones of the current leads; a voltage transformer connected tosaid two different ones of said current leads, a plurality of resistors,said current transformers having secondary windings shunted by saidresistors having resistances proportional to the total resistance of thecorresponding current lead and being connected in series to each otherand to the secondary windings of the voltage transformer, the output ofthe transducer being essentially a geometrical sum of the voltagesacross the current leads and the voltage drop across said current leadsbeing proportional to the motor voltage; a comparison unit adapted tocompare a reference voltage proportional to the voltage to be stabilizedwith the output voltage of said transducer, the output of saidcomparison unit being connected to the voltage control unit forcontrolling the operation of said control unit.
 2. A device as claimedin Claim 3, wherein the resistance of each of the shunting resistors iswhere, Z is the total resistance of the wire to which the resistor isconnected, Ki stands for the transformation ratio of the currenttransformer, and Ku is the transformation ratio of the voltagetransformer.
 3. A device as claimed in claim 1, wherein said pluralityof resistors are variable.
 4. A device as claimed in claim 1, includinga full wave rectifier connected across the output of said transducer, afilter coupled between said transducer and said comparison unit.